This invention relates to an oxygen indicator, and particularly relates to an oxygen indicator comprising at least one dyestuff, at least one alkaline substance and at least one reducing agent. In the present oxygen indicator, the color of the oxygen indicator in an aerobic atmosphere differs from the color thereof in an anaerobic atmosphere. So, whether oxygen is present or not in the atmosphere in which the indicator is placed is easily determined by its reversible color change.
An oxygen indicator, which comprises an aqueous solution of sodium hydroxide, glucose and Methylene Blue has been known to the art.
Recently, oxygen-free packaging of foodstuffs, e.g. vacuum-package, oxygen absorption package, nitrogen-sealing package, and so on, is widely employed in order to prolong the shelf-life of the foodstuff. So, a convenient oxygen indicator which has high sensitivity and long life is necessitated for the control of such packing systems. However the life of the oxygen indicator in the prior art is too short to be used for such a purpose.